Water is one of the most important molecules on the planet. It is seemingly everywhere. Two-thirds of our planet is covered by water. Water is in the air making clouds and determining our weather. Water is essential for virtually every living thing. Have you ever really thought about where all that water comes from? Where it goes? What happens to it?

Water never really leaves. It only changes forms. The water that was in your milk this morning is the same water that was around millions of years ago. You may have actually been drinking water that was once water for a dinosaur. Water is constantly being recycled in a process called the water cycle.

Let's follow the path of a water molecule as it goes through the water cycle. The water molecule could have started in a lake. Some of the water in the lake will stay there for a long time. Some of the water will evaporate into the atmosphere to eventually form clouds. Some water will sink into the ground to be used by plants like trees. The water that gets to the tree's roots will move up the tree till it gets to a leaf. When the water gets to the leaves, it will either get put into a sugar molecule, or it will evaporate. Evaporation from the leaves of plants is called transpiration.

When water gets into the atmosphere- be it from evaporation or transpiration- it is in a gaseous form. This water vapor collects together to form clouds. The clouds get bigger and heavier until they eventually burst and send rain down to the ground. The rain then runs into lakes or streams, and the cycle starts all over. It never stops.